Friday, June 26, 2009

Catching Fire: How Cooking Made Us Human Fat

I finished Catching Fire: How Cooking Made Us Human earlier this week, and as I mentioned previously, was planning on writing up a full review. I may still do it, but as I was thinking about how to structure the post, one particular aspect of the book kept jumping out at me as something I wanted to write about. Before I get to that, I will say that it's quite an interesting book that is really well written... it's also pretty short with little over 200 pages of text (lots of footnotes though). Read it, and your mastery of a provacative and controversial theory of human evolution will amaze your friends at dinner parties!

Now then, the basic theory presented is detailed better elsewhere, but in short, the idea is that our ancestors started cooking a lot earlier than is commonly believed. Wrangham asserts that, indeed, it was cooking itself that propelled habilines to Homo erectus to Homo sapiens. He cites massive changes in the digestive system along that evolutionary path and speculates that the reduced digestion cost was used to create bigger brains, which could only be accomplished through cooked food. And now we get to the really interesting part... the part that intersects people like Michael Pollan and the slow food movement.

The obvious question is: what difference does cooking make? Doesn't a raw carrot have the same amount of calories as a cooked carrot? Well yes it does (give or take). But calories are only part of the story, as our digestive system extracts much more energy from cooked food. This isn't true just of humans, but even our own pets whose food comes cooked from PETCO and who often look a lot rounder than seen in nature. Everything from flies to rats to pythons have been shown to gain much more weight on a diet of cooked food. We're different from those animals in that we've been so adapted to this extra energy gained from eating cooked food, that people in the Raw Food movement invariably loose a ton of weight, women stop menstruating, and they all feel really hungry all the time because our bodies just can't extract enough energy out of uncooked food.

It doesn't stop at just at cooking though... processing in general... makes food easier to digest and allows more calories to be used by our bodies. If you take the same amount of calories of cooked food in two batches, but grind one up and leave the other whole, you'll get more energy from the ground up batch. This was most ably demonstrated by the study Wrangham cited by Oka et al, where rats were given pellets that were either hard or soft(requiring more or less chewing). Even though both groups of rats consumed the same amount of calories, the rats on the soft diet gained more weight... seemingly from the fact that they generated less body heat, and thus had expended less energy, digesting their food. He presented other examples, but I'll leave it to you to read the book if you're interested in seeing more support for the argument... I imagine most people who would stumble across this post probably already agree that there is something about our modern Western diet, and it's heavily processed nature, that is making us fat. Before Wrangham's hypothesis, I had found most of explanations of why this might be to be fairly unsatisfactory. Yeah, I'm sure there's something to the idea that these refined sugars are almost like a drug that we can't stop longing for, and how we just don't notice how much we've eaten of them.... but it mainly amounts to saying there is just something "wrong" about these foods, even if we don't know exactly what it is. Well what if it's this: processing allows you to extract more calories from your food. Calories aren't calories when you don't take into account how digestible the food in question is.

Unfortunately, it doesn't look like we're very close to getting a real measurement of how much we extract from any particular food... nor even a model to estimate it. I don't imagine Hostess is going to be clamoring for a revision of food labels that would make them look even worse for you than they already do. In the end, I guess we're still left with "eat food, not too much, mostly plants" and the like... but, I at least, find this rationale for why infinitely more satisfying.

photo by flicker user patries71 used under a Creative Commons license